Molecular sieve SSZ-91, methods for preparing SSZ-91, and uses for SSZ-91

ABSTRACT

A family of new crystalline molecular sieves designated SSZ-91 is disclosed, as are methods for making SSZ-91 and uses for SSZ-91. Molecular sieve SSZ-91 is structurally similar to sieves falling within the ZSM-48 family of molecular sieves, and is characterized as: (1) having a low degree of faulting, (2) a low aspect ratio that inhibits hydrocracking as compared to conventional ZSM-48 materials having an aspect ratio of greater than 8, and (3) is substantially phase pure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/753,074, filed on Feb. 15, 2018, now U.S. Pat. No. 10,618,816, whichis a 371 (c)(1) filing based on PCT Appl. No. PCT/US2016/046614, filedon Aug. 11, 2016, and a continuation of U.S. patent application Ser. No.14/837,071, filed on Aug. 27, 2015, now U.S. Pat. No. 9,802,830, and acontinuation of U.S. patent application Ser. No. 14/837,087, filed onAug. 27, 2015, now abandoned, and a continuation of U.S. patentapplication Ser. No. 14/837,094, filed on Aug. 27, 2015, now abandoned,and a continuation of U.S. patent application Ser. No. 14/837,108, filedon Aug. 27, 2015, now U.S. Pat. No. 9,920,260, all herein incorporatedin their entirety.

TECHNICAL FIELD

Described herein is a new family of crystalline molecular sievesdesignated as SSZ-91, methods for preparing SSZ-91 and uses for SSZ-91.

BACKGROUND

Because of their unique sieving characteristics, as well as theircatalytic properties, crystalline molecular sieves and molecular sievesare especially useful in applications such as hydrocarbon conversion,gas drying and separation. Although many different crystalline molecularsieves have been disclosed, there is a continuing need for new molecularsieves with desirable properties for gas separation and drying,hydrocarbon and chemical conversions, and other applications. Newmolecular sieves may contain novel internal pore architectures,providing enhanced selectivities in these processes.

Molecular sieves have distinct crystal structures which are demonstratedby distinct X-ray diffraction patterns. The crystal structure definescavities and pores which are characteristic of the different species.

Molecular sieves are classified by the Structure Commission of theInternational Zeolite Association according to the rules of the IUPACCommission on Zeolite Nomenclature. According to this classification,framework type zeolites and other crystalline microporous molecularsieves, for which a structure has been established, are assigned a threeletter code and are described in the “Atlas of Zeolite Framework Types”Sixth Revised Edition, Elsevier (2007) and the Database of Molecularsieve Structures on the International Zeolite Association's website(http://www.iza-online.org).

The structure of a molecular sieve can be either ordered or disordered.Molecular sieves having an ordered structure have periodic buildingunits (PerBUs) that are periodically ordered in all three dimensions.Structurally disordered structures show periodic ordering in dimensionsless than three (i.e., in two, one or zero dimensions). Disorder occurswhen the PerBUs connect in different ways, or when two or more PerBUsintergrow within the same crystal. Crystal structures built from PerBUsare called end-member structures if periodic ordering is achieved in allthree dimensions.

In disordered materials, planar stacking faults occur where the materialcontains ordering in two dimensions. Planar faults disrupt the channelsformed by the material's pore system. Planar faults located near thesurface limit diffusion pathways otherwise required in order to allowfeedstock components to access the catalytically active portions of thepore system. Therefore, as the degree of faulting increases, thecatalytic activity of the material typically decreases.

In the case of crystals with planar faults, interpretation of X-raydiffraction patterns requires an ability to simulate the effects ofstacking disorder. DIFFaX is a computer program based on a mathematicalmodel for calculating intensities from crystals containing planarfaults. (See, M. M. J. Treacy et al., Proceedings of the Royal ChemicalSociety, London, A (1991), Vol. 433, pp. 499-520). DIFFaX is thesimulation program selected by and available from the InternationalZeolite Association to simulate the XRD powder patterns for intergrownphases of molecular sieves. (See “Collection of Simulated XRD PowderPatterns for Zeolites” by M. M. J. Treacy and J. B. Higgins, 2001,Fourth Edition, published on behalf of the Structure Commission of theInternational Zeolite Association). It has also been used totheoretically study intergrown phases of AEI, CHAand KFI molecularsieves, as reported by K. P. Lillerud et al. in “Studies in SurfaceScience and Catalysis”, 1994, Vol. 84, pp. 543-550. DIFFaX is awell-known and established method to characterize disordered crystallinematerials with planar faults such as intergrown molecular sieves.

The designation ZSM-48 refers to a family of disordered materials, eachcharacterized as having a one-dimensional 10-ring tubular pore system.The pores are formed of rolled up honeycomb-like sheets of fusedtetrahedral 6-ring structures, and the pore aperture contains 10tetrahedral-atoms. Zeolites EU-2, ZSM-30 and EU-11 fall into the ZSM-48family of zeolites.

According to Lobo and Koningsveld, the ZSM-48 family of molecular sievesconsists of nine polytypes. (See J. Am. Chem. Soc. 2002, 124,13222-13230). These materials have very similar, but not identical,X-ray diffraction patterns. The Lobo and Koningsveld paper describestheir analysis of three ZSM-48 samples provided by Dr. AlexanderKuperman of Chevron Corporation. Each of the three samples, labeledSamples A, B and C, respectively, were prepared using three differentstructure directing agents. Comparative Examples 2 and 3 herein belowcorrespond to Samples A and B described in the Lobo and Koningsveldpaper.

The Lobo and Koningsveld paper describes Sample A as being polytype 6,and Sample B as being a faulted polytype 6. The paper further describesthe morphology of Sample A as consisting of needle-like crystals havinga diameter of ^(˜)20 nm and a length of ^(˜)0.5 μm. The morphology ofSample B consisted of long, narrow crystals having a width of ^(˜)0.5 μmand a length of 4-8 μm. As indicated in Comparative Examples 2 and 3below, the scanning electron microscopy images for Samples A and B arepresented herein in FIGS. 3 and 4.

Kirschhock and co-workers describe the successful synthesis ofphase-pure polytype 6. (See, Chem. Mater. 2009, 21, 371-380). In theirpaper, Kirschhock and co-workers describe their phase-pure polytype 6material (which they refer to as COK-8) as having a morphologyconsisting of long needle-like crystals (width, 15-80 nm; length, 0.5-4μm) with a very large length/width ratio, growing along theinterconnecting pore direction.

As indicated in the Kirschhock paper, molecular sieves from the ZSM-48family of molecular sieves consist of 10-ring, 1-dimensional porestructures, wherein the channels formed by the interconnected poresextend perpendicular to the long axis of the needles. Therefore, thechannel openings are located at the short ends of the needles. As thelength-to-diameter ratio (also known as aspect ratio) of these needlesincreases, so does the diffusion pathway for the hydrocarbon feed. Asthe diffusion pathway increases, so does the residence time of the feedin the channels. A longer residence time results in increasedundesirable hydrocracking of the feed with a concomitant reduction inselectivity.

Accordingly, there is a current need for ZSM-48 molecular sieves whichexhibit lower degree of hydrocracking over known ZSM-48 molecularsieves. There is also a continuing need for ZSM-48 molecular sieveswhich are phase pure or substantially phase-pure, and have a low degreeof disorder within the structure (a low degree of faulting).

SUMMARY

Described herein below is a family of crystalline molecular sieves withunique properties, referred to herein as “molecular sieve SSZ-91” orsimply “SSZ-91.” Molecular sieve SSZ-91 is structurally similar tosieves falling within the ZSM-48 family of zeolites, and ischaracterized as: (1) having a low degree of faulting, (2) a low aspectratio that inhibits hydrocracking as compared to conventional ZSM-48materials having an aspect ratio of greater than 8, and (3) issubstantially phase pure.

As will be shown in the Examples below, a ZSM-48 material lacking anyone of the three uniquely combined characteristics of SSZ-91 (low aspectratio, low EU-1 content, high polytype 6 composition) will exhibit poorcatalytic performance.

In one aspect, there is provided a molecular sieve having a mole ratioof 40 to 200 of silicon oxide to aluminum oxide. In its as-made form,the X-ray diffraction lines of Table 2 herein are indicative of SSZ-91.

SSZ-91 materials are composed of at least 70% polytype 6 of the totalZSM-48-type material present in the product, as determined by DIFFaXsimulation and as described by Lobo and Koningsveld in J. Am. Chem. Soc.2012, 124, 13222-13230, where the disorder was tuned by three distinctfault probabilities. It should be noted the phrase “at least 70%”includes the case where there are no other ZSM-48 polytypes present inthe structure, i.e., the material is 100% phase-pure polytype 6.

In another aspect, SSZ-91 is substantially phase pure. SSZ-91 containsan additional EUO-type molecular sieve phase in an amount of between 0and 3.5 percent by weight (inclusive) of the total product.

Molecular sieve SSZ-91 has a morphology characterized as polycrystallineaggregates, each of the aggregates being characterized as being composedof crystallites collectively having an average aspect ratio of between 1and 8 (inclusive). SSZ-91 exhibits a lower degree of hydrocracking thanthose ZSM-48 materials having a higher aspect ratio. An aspect ratio of1 is the ideal lowest value, where the length and width are the same.

In another aspect, there is provided a method of preparing a crystallinematerial by contacting under crystallization conditions (1) at least onesource of silicon oxide; (2) at least one source of aluminum oxide; (3)at least one source of an element selected from Groups 1 and 2 of thePeriodic Table; (4) hydroxide ions; and (5) hexamethonium cations.

In yet another aspect, there is provided a process for preparing acrystalline material having, as made, the X-ray diffraction lines ofTable 2, by:

(a) preparing a reaction mixture containing (1) at least one source ofsilicon oxide; (2) at least one source of aluminum oxide; (3) at leastone source of an element selected from Groups 1 and 2 of the PeriodicTable; (4) hydroxide ions; (5) hexamethonium cations; and (6) water; and

(b) maintaining the reaction mixture under crystallization conditionssufficient to form crystals of the molecular sieve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a powder X-ray diffraction (XRD) pattern of as-synthesizedmolecular sieve prepared in Comparative Example 1.

FIG. 2 is a scanning electron micrograph of as-synthesized molecularsieve prepared in Comparative Example 1.

FIG. 3 is a scanning electron micrograph of as-synthesized molecularsieve prepared in Comparative Example 2.

FIG. 4 is a scanning electron micrograph of as-synthesized molecularsieve prepared in Comparative Example 3.

FIG. 5 is a powder XRD pattern of as-synthesized molecular sieve SSZ-91prepared in Example 7.

FIG. 6 is a scanning electron micrograph of as-synthesized molecularsieve SSZ-91 prepared in Example 7.

FIG. 7 is a scanning electron micrograph of as-synthesized molecularsieve prepared in Example 8.

FIG. 8 is a plot of several DIFFaX-generated simulated XRD patterns anda powder XRD pattern of the as-synthesized molecular sieve SSZ-91prepared in Example 8.

FIG. 9 is a plot of several DIFFaX-generated simulated XRD patterns anda powder XRD pattern of the as-synthesized molecular sieve prepared inExample 11.

FIG. 10 is a plot of several DIFFaX-generated simulated XRD patterns anda powder XRD pattern of the as-synthesized molecular sieve prepared inComparative Example 1.

FIG. 11 is a scanning electron micrograph of as-synthesized molecularsieve prepared in Example 13.

FIG. 12 is a plot of several DIFFaX-generated simulated XRD patterns anda powder XRD pattern of the as-synthesized molecular sieve prepared inExample 13.

DETAILED DESCRIPTION Introduction

The term “active source” means a reagent or precursor material capableof supplying at least one element in a form that can react and which canbe incorporated into the molecular sieve structure. The terms “source”and “active source” can be used interchangeably herein.

The term “molecular sieve” and “zeolite” are synonymous and include (a)intermediate and (b) final or target molecular sieves and molecularsieves produced by (1) direct synthesis or (2) post-crystallizationtreatment (secondary modification). Secondary synthesis techniques allowfor the synthesis of a target material from an intermediate material byheteroatom lattice substitution or other techniques. For example, analuminosilicate can be synthesized from an intermediate borosilicate bypost-crystallization heteroatom lattice substitution of the Al for B.Such techniques are known, for example as described in U.S. Pat. No.6,790,433 to C. Y. Chen and Stacey Zones, issued Sep. 14, 2004.

The term “*MRE-type molecular sieve” and “EUO-type molecular sieve”includes all molecular sieves and their isotypes that have been assignedthe International Zeolite Association framework, as described in theAtlas of Zeolite Framework Types, eds. Ch. Baerlocher, L. B. McCuskerand D. H. Olson, Elsevier, 6^(th) revised edition, 2007 and the Databaseof Zeolite Structures on the International Zeolite Association's website(http://www.iza-online.org).

The term “Periodic Table” refers to the version of IUPAC Periodic Tableof the Elements dated Jun. 22, 2007, and the numbering scheme for thePeriodic Table Groups is as described in Chem. Eng. News, 63(5), 26-27(1985).

For the purposes of this specification and appended claims, unlessotherwise indicated, all numbers expressing quantities, percentages orproportions, and other numerical values used in the specification andclaims, are to be understood as being modified in all instances by theterm “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that can vary depending upon thedesired properties sought to be obtained. It is noted that, as used inthis specification and the appended claims, the singular forms “a,”“an,” and “the,” include plural references unless expressly andunequivocally limited to one referent. As used herein, the term“include” and its grammatical variants are intended to be non-limiting,such that recitation of items in a list is not to the exclusion of otherlike items that can be substituted or added to the listed items. As usedherein, the term “comprising” means including elements or steps that areidentified following that term, but any such elements or steps are notexhaustive, and an embodiment can include other elements or steps.

Unless otherwise specified, the recitation of a genus of elements,materials or other components, from which an individual component ormixture of components can be selected, is intended to include allpossible sub-generic combinations of the listed components and mixturesthereof. In addition, all number ranges presented herein are inclusiveof their upper and lower limit values.

The patentable scope is defined by the claims, and can include otherexamples that occur to those skilled in the art. Such other examples areintended to be within the scope of the claims if they have structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal languages of the claims. To an extent notinconsistent herewith, all citations referred to herein are herebyincorporated by reference.

Reaction Mixture and Crystallization

In preparing SSZ-91, at least one organic compound selective forsynthesizing molecular sieves from the ZSM-48 family of zeolites is usedas a structure directing agent (“SDA”), also known as a crystallizationtemplate. The SDA useful for making SSZ-91 is represented by thefollowing structure (1):

The SDA cation is typically associated with anions which may be anyanion that is not detrimental to the formation of the molecular sieve.Representative examples of anions include hydroxide, acetate, sulfate,carboxylate and halogens, for example, fluoride, chloride, bromide andiodide. In one embodiment, the anion is bromide.

In general, SSZ-91 is prepared by:

(a) preparing a reaction mixture containing (1) at least one source ofsilicon oxide; (2) at least one source of aluminum oxide; (3) at leastone source of an element selected from Groups 1 and 2 of the PeriodicTable; (4) hydroxide ions; (5) hexamethonium cations; and (6) water; and

(b) maintaining the reaction mixture under crystallization conditionssufficient to form crystals of the molecular sieve.

The composition of the reaction mixture from which the molecular sieveis formed, in terms of mole ratios, is identified in Table 1 below:

TABLE 1 Components Broad Exemplary SiO₂/Al₂O₃   50-220   85-180 M/SiO₂0.05-1.0  0.1-0.8 Q/SiO₂ 0.01-0.2 0.02-0.1 OH/SiO₂ 0.05-0.4 0.10-0.3H₂O/SiO₂   3-100   10-50wherein,

-   -   (1) M is selected from the group consisting of elements from        Groups 1 and 2 of the Periodic Table; and    -   (2) Q is the structure directing agent represented by structure        1 above.

Sources useful herein for silicon include fumed silica, precipitatedsilica, silica hydrogel, silicic acid, colloidal silica, tetra-alkylorthosilicates (e.g., tetraethyl orthosilicate), and silica hydroxides.

Sources useful herein for aluminum include aluminates, alumina, andaluminum compounds such as AlCl₃, Al₂(SO₄)₃, Al(OH)₃, kaolin clays, andother zeolites. An example of the source of aluminum oxide is LZ-210zeolite (a type of Y zeolite).

As described herein above, for each embodiment described herein, thereaction mixture can be formed containing at least one source of anelements selected from Groups 1 and 2 of the Periodic Table (referred toherein as M). In one sub-embodiment, the reaction mixture is formedusing a source of an element from Group 1 of the Periodic Table. Inanother sub-embodiment, the reaction mixture is formed using a source ofsodium (Na). Any M-containing compound which is not detrimental to thecrystallization process is suitable. Sources for such Groups 1 and 2elements include oxide, hydroxides, nitrates, sulfates, halides,oxalates, citrates and acetates thereof.

For each embodiment described herein, the molecular sieve reactionmixture can be supplied by more than one source. Also, two or morereaction components can be provided by one source.

The reaction mixture can be prepared either batch wise or continuously.Crystal size, morphology and crystallization time of the molecular sievedescribed herein can vary with the nature of the reaction mixture andthe crystallization conditions.

The reaction mixture is maintained at an elevated temperature until thecrystals of the molecular sieve are formed. In general, zeolitehydrothermal crystallization is usually conducted under pressure, andusually in an autoclave so that the reaction mixture is subject toautogenous pressure and optionally stirring, at a temperature between125° C. and 200° C., for a period of 1 to more than 18 hours.

As noted herein above, SSZ-91 is a substantially phase pure material. Asused herein, the term “substantially phase pure material” means thematerial is completely free of zeolite phases other than those belongingto the ZSM-48 family of zeolites, or are present in quantities that haveless than a measureable effect on, or confer less than a materialdisadvantage to, the selectivity of the material. Two common phases thatco-crystalize with SSZ-91 are EUO-type molecular sieves such as EU-1, aswell as Magadiite and Kenyaite. These additional phases may be presentas separate phases, or may be intergrown with the SSZ-91 phase. Asdemonstrated in the Examples below, the presence of high amounts of EU-1in the product is deleterious to the selectivity for hydroisomerizationby SSZ-91.

In one embodiment, the SSZ-91 product contains an additional EUO-typemolecular sieve phase in an amount of between 0 and 3.5 percent byweight. In one subembodiment, SSZ-91 contains between 0.1 and 2 wt. %EU-1. In another subembodiment, SSZ-91 contains between 0.1 and 1 wt. %EU-1.

It's known that the ratio of powder XRD peak intensities varies linearlyas a function of weight fractions for any two phases in a mixture:(Iα/Iβ)=(RIRα/RIRβ)*(xα/xβ), where the RIR (Reference Intensity Ratio)parameters can be found in The International Centre for DiffractionData's Powder Diffraction File (PDF) database(http://www.icdd.com/products/). The weight percentage of the EUO phaseis therefore calculated by measuring the ratio between the peakintensity of the EUO phase and that of the SSZ-91 phase.

The formation of amounts of the EUO phase is suppressed by selecting theoptimal hydrogel composition, temperature and crystallization time whichminimizes the formation of the EUO phase while maximizing the SSZ-91product yield. The Examples below provide guidance on how changes inthese process variables minimize the formation of EU-1. A zeolitemanufacturer with ordinary skill in the art will readily be able toselect the process variables necessary to minimize the formation ofEU-1, as these variables will depend on the size of the production run,the capabilities of the available equipment, desired target yield andacceptable level of EU-1 material in the product.

During the hydrothermal crystallization step, the molecular sievecrystals can be allowed to nucleate spontaneously from the reactionmixture. The use of crystals of the molecular sieve as seed material canbe advantageous in decreasing the time necessary for completecrystallization to occur. In addition, seeding can lead to an increasedpurity of the product obtained by promoting the nucleation and/orformation of the molecular sieve over any undesired phases. However, ithas been found that if seeding is employed, the seeds must be veryphase-pure SSZ-91 to avoid the formation of a large amount of a EUOphase. When used as seeds, seed crystals are added in an amount between0.5% and 5% of the weight of the silicon source used in the reactionmixture.

The formation of Magadiite and Kenyaite is minimized by optimizing thehexamethonium bromide/SiO₂ ratio, controlling the hydroxideconcentration, and minimizing the concentration of sodium as Magadiiteand Kenyaite are layered sodium silicate compositions. The Examplesbelow provide guidance on how changes in gel conditions minimize theformation of EU-1.

Once the molecular sieve crystals have formed, the solid product isseparated from the reaction mixture by standard mechanical separationtechniques such as filtration. The crystals are water-washed and thendried to obtain the as-synthesized molecular sieve crystals. The dryingstep can be performed at atmospheric pressure or under vacuum.

Post-Crystallization Treatment

The molecular sieve can be used as-synthesized, but typically will bethermally treated (calcined). The term “as-synthesized” refers to themolecular sieve in its form after crystallization, prior to removal ofthe SDA cation. The SDA can be removed by thermal treatment (e.g.,calcination), preferably in an oxidative atmosphere (e.g., air, gas withan oxygen partial pressure of greater than 0 kPa) at a temperaturereadily determinable by one skilled in the art sufficient to remove theSDA from the molecular sieve. The SDA can also be removed by ozonationand photolysis techniques (e.g., exposing the SDA-containing molecularsieve product to light or electromagnetic radiation that has awavelength shorter than visible light under conditions sufficient toselectively remove the organic compound from the molecular sieve) asdescribed in U.S. Pat. No. 6,960,327.

The molecular sieve can subsequently be calcined in steam, air or inertgas at temperatures ranging from 200° C. to 800° C. for periods of timeranging from 1 to 48 hours, or more. Usually, it is desirable to removethe extra-framework cation (e.g., Na⁺) by ion exchange and replace itwith hydrogen, ammonium, or any desired metal-ion.

Where the molecular sieve formed is an intermediate molecular sieve, thetarget molecular sieve can be achieved using post-synthesis techniquessuch as heteroatom lattice substitution techniques. The target molecularsieve (e.g., silicate SSZ-91) can also be achieved by removingheteroatoms from the lattice by known techniques such as acid leaching.

The molecular sieve made from the process disclosed herein can be formedinto a wide variety of physical shapes. Generally speaking, themolecular sieve can be in the form of a powder, a granule, or a moldedproduct, such as extrudate having a particle size sufficient to passthrough a 2-mesh (Tyler) screen and be retained on a 400-mesh (Tyler)screen. In cases where the catalyst is molded, such as by extrusion withan organic binder, the molecular sieve can be extruded before drying,or, dried or partially dried and then extruded.

The molecular sieve can be composited with other materials resistant tothe temperatures and other conditions employed in organic conversionprocesses. Such matrix materials include active and inactive materialsand synthetic or naturally occurring molecular sieves as well asinorganic materials such as clays, silica and metal oxides. Examples ofsuch materials and the manner in which they can be used are disclosed inU.S. Pat. Nos. 4,910,006 and 5,316,753.

The extrudate or particle may then be further loaded using a techniquesuch as impregnation or ion-exchange, with one or more active metalsselected from the group consisting of metals from Groups 8 to 10 of thePeriodic Table, to enhance the hydrogenation function. It may bedesirable to co-impregnate a modifying metal and one or more Group 8 to10 metals at once, as disclosed in U.S. Pat. No. 4,094,821. In oneembodiment, the at least one active metal is selected from the groupconsisting of nickel, platinum, palladium, and combinations thereof.After metal loading, the metal loaded extrudate or particle can becalcined in air or inert gas at temperatures from 200° C. to 500° C. Inone embodiment, the metal loaded extrudate is calcined in air or inertgas at temperatures from 390° C. to 482° C.

SSZ-91 is useful for a variety of hydrocarbon conversion reactions suchas hydrocracking, dewaxing, olefin isomerization, alkylation andisomerization of aromatic compounds and the like. SSZ-91 is also usefulas an adsorbent for general separation purposes.

Characterization of the Molecular Sieve

Molecular sieves made by the process disclosed herein have SiO₂/Al₂O₃mole ratio (SAR) of 40 to 200. The SAR is determined by inductivelycoupled plasma (ICP) elemental analysis. In one subembodiment, SSZ-91has a SAR of between 70 and 160. In another subembodiment, SSZ-91 has aSAR of between 80 and 140.

SSZ-91 materials are composed of at least 70% polytype 6 of the totalZSM-48-type material present in the product, as determined by DIFFaXsimulation and as described by Lobo and Koningsveld in J. Am. Chem. Soc.2012, 124, 13222-13230, where the disorder was tuned by three distinctfault probabilities. It should be noted the phrase “at least X %”includes the case where there are no other ZSM-48 polytypes present inthe structure, i.e., the material is 100% polytype 6. The structure ofpolytype 6 is as described by Lobo and Koningsveld. (See. Am. Chem. Soc.2002, 124, 13222-13230). In one embodiment, the SSZ-91 material iscomposed of at least 80% polytype 6 of the total ZSM-48-type materialpresent in the product. In another embodiment, the SSZ-91 material iscomposed of at least 90% polytype 6 of the total ZSM-48-type materialpresent in the product. The polytype 6 structure has been given theframework code *MRE by the Structure Commission of the InternationalZeolite Association.

Molecular sieve SSZ-91 has a morphology characterized as polycrystallineaggregates having a diameter of between about 100 nm and 1.5 μm, each ofthe aggregates comprising a collection of crystallites collectivelyhaving an average aspect ratio of between 1 and 8. As used herein, theterm diameter refers to the shortest length on the short end of eachcrystallite examined. SSZ-91 exhibits a lower degree of hydrocrackingthan those ZSM-48 materials having a higher aspect ratio. In onesubembodiment, the average aspect ratio is between 1 and 5. In anothersubembodiment, the average aspect ratio is between 1 and 4. In yetanother subembodiment, the average aspect ratio is between 1 and 3.

Molecular sieves synthesized by the process disclosed herein can becharacterized by their XRD pattern. The powder XRD lines of Table 2 arerepresentative of as-synthesized SSZ-91 made in accordance with themethods described herein. Minor variations in the diffraction patterncan result from variations in the mole ratios of the framework speciesof the particular sample due to changes in lattice constants. Inaddition, sufficiently small crystals will affect the shape andintensity of peaks, leading to significant peak broadening. Minorvariations in the diffraction pattern can also result from variations inthe organic compound used in the preparation and from variations in theSi/AI mole ratio from sample to sample. Calcination can also cause minorshifts in the XRD pattern. Notwithstanding these minor perturbations,the basic crystal lattice structure remains unchanged.

TABLE 2 Characteristic Peaks for As-Synthesized SSZ-91 2-Theta^((a))d-spacing (nm) Relative Intensity^((b)) 7.55 1.170 W 8.71 1.015 W 12.490.708 W 15.12 0.586 W 21.18 0.419 VS 22.82 0.390 VS 24.62 0.361 W 26.390.337 W 29.03 0.307 W 31.33 0.285 W ^((a))± 0.20

-   -   ^((b))The powder XRD patterns provided are based on a relative        intensity scale in which the strongest line in the X-ray pattern        is assigned a value of 100: W=weak (>0 to ≤20); M=medium (>20 to        ≤40); S=strong (>40 to ≤60); VS=very strong (>60 to ≤100).

The X-ray diffraction pattern lines of Table 3 are representative ofcalcined SSZ-91 made in accordance with the methods described herein.

TABLE 3 Characteristic Peaks for Calcined SSZ-91 2-Theta^((a)) d-spacing(nm) Relative Intensity^((b)) 7.67 1.152 M 8.81 1.003 W 12.61 0.701 W15.30 0.579 W 21.25 0.418 VS 23.02 0.386 VS 24.91 0.357 W 26.63 0.334 W29.20 0.306 W 31.51 0.284 W ^((a))± 0.20 ^((b))The powder XRD patternsprovided are based on a relative intensity scale in which the strongestline in the X-ray pattern is assigned a value of 100: W = weak (>0 to≤20); M = medium (>20 to ≤40); S = strong (>40 to ≤60); VS = very strong(>60 to ≤100).

The powder X-ray diffraction patterns presented herein were collected bystandard techniques. The radiation was CuK_(α) radiation. The peakheights and the positions, as a function of 2θ where θ is the Braggangle, were read from the relative intensities of the peaks (adjustingfor background), and d, the interplanar spacing corresponding to therecorded lines, can be calculated.

EXAMPLES

The following illustrative examples are intended to be non-limiting.

SUMMARY OF THE EXAMPLES

The Examples below demonstrate that a ZSM-48 material lacking any one ofthe three uniquely combined characteristics of SSZ-91 (low aspect ratio,low EU-1 content, high polytype 6 composition) will exhibit poorcatalytic performance. Table 4 below summarizes the hydroprocessingperformance for various Examples outlined below. Only Example 8 (SSZ-91)exhibited superior performance, namely superior selectivity and low gasmake as compared to the other three Examples. The remaining materialstested in the other three Examples exhibited poor performance becauseeach lacked at least one of the three uniquely combined characteristicsthat define SSZ-91.

TABLE 4 % Aspect Isomerization Polytype % Selectivity at 96% C₄ ⁻Examples 6 EU-1 Ratio (n-C₁₆ Conversion) Cracking Comparative 80 <1 7-12 78% 2.8% Example 1 Example 8 >90 3.20 1-4 87% 1.5% Example 11 >906.82 2-6 82% 2.6% Example 13 >90 3.16  9-15 78% 2.2%

Comparative Example 1 Synthesis of ZSM-48

The product in this Example was prepared according to the teachings ofU.S. Pat. No. 5,075,269 to Thomas F. Degnan and Ernest W. Valyocsik(Mobil Oil Corp.) issued Dec. 24, 1991, using available reagents.

Into a 1-gallon autoclave liner were added 76.51 g of NaOH (50%), 846 gof de-ionized water, 124.51 g of HI-SIL 233 silica (PPG Industries), and63 g of hexamethonium bromide (“HMB,” Sigma Aldrich). After all thesolids had dissolved, 396 g of aluminum stock solution prepared bydissolving 4.35 g Al₂(SO₄)₃.18H₂O and 63 g conc. H₂SO₄ in 733.52 gde-ionized water, was added. Finally, 0.45 g of SSZ-91 seed crystalsfrom Example 7 was added. The mixture was stirred until homogeneous. Thecomposition of the aluminosilicate gel produced had the following moleratios:

TABLE 5 SiO₂/Al₂O₃ 220 H₂O/SiO₂ 39.9 OH⁻/SiO₂ 0.21 Na⁺/SiO₂ 0.56HMB/SiO₂ 0.10 Seed 0.38%

The liner was transferred to a 1-gallon autoclave, which was heated to160° C. over a period of 8 hours, and stirred at a rate of 150 rpm atautogenous pressure. After 80 hours, the product was filtered, washedwith de-ionized water and dried. The resulting solids were determined byXRD to be a ZSM-48 material (FIG. 1). The XRD indicated there was animmeasurable amount of EU-1 in the product (likely less than 1% EU-1).The SEM shows agglomerated long needles of ZSM-48 crystals (FIG. 2),with an aspect ratio of 7-12.

Comparative Examples 2 and 3

As noted above, the Lobo and Koningsveld paper describes their analysisof three ZSM-48 samples provided by Dr. Alexander Kuperman of ChevronCorporation. Each of the three samples, Samples A, B and C,respectively, were prepared using three different structure directingagents. The Lobo and Koningsveld paper describes Sample A as beingpolytype 6, and Sample B as being a faulted polytype 6. The paperfurther describes the morphology of Sample A (FIG. 3) of consisting ofthin needle-like crystals having a diameter of ^(˜)20 nm and a length of^(˜)0.5 μm. The morphology of Sample B (FIG. 4) consisted of long,narrow crystals having a diameter of ^(˜)30 nm and a length of 4-8 μm.Even though Dr. Kuperman's materials were reported as having a highconcentration of polytype 6, the samples are characterized as havingaspect ratios (length/diameter) of 25 for Sample A, and an aspect ratioranging between 133 and 266 for Sample B.

Examples 4-11 Synthesis of SSZ-91 with Varying EU-1 Concentrations inthe Product

Each of Examples 4 through 11 were prepared by adding NaOH (50%),de-ionized water, HI-SIL 233 silica (PPG Industries), hexamethoniumbromide (Sigma Aldrich) to an autoclave liner. After all the solids haddissolved, an aluminum stock solution prepared by dissolving 4.18 gAl₂(SO₄)₃.18H₂O and 45.58 g conc. H₂SO₄ in 540.6 g de-ionized water, wasadded. The mixture was stirred until homogeneous. The mole ratios forthe aluminosilicate gels and heating periods are listed in Table 6below.

TABLE 6 Example No. 4 5 6 7 8 9 10 11 SiO₂/Al₂O₃ 218.6 113.6 177.8 180177.7 177.7 177.7 170.0 H₂O/SiO₂ 40.0 23.0 40.3 40.0 40.3 40.3 40.3 40OH⁻/SiO₂ 0.21 0.17 0.27 0.28 0.27 0.27 0.27 0.27 Na⁺/SiO₂ 0.56 0.17 0.210.71 0.71 0.71 0.71 0.46 HMB/SiO₂ 0.10 0.02 0.10 0.10 0.10 0.10 0.100.10 Crystallization 38 48 30 34 30 30 30 30 Period (hrs)

The liner was transferred to an autoclave, which was heated to 160° C.over a period of 8 hours, and stirred at a rate of 150 rpm at autogenouspressure. After the crystallization period, the product was filtered,washed with de-ionized water and dried. The resulting solids wereanalyzed by XRD to determine the product and the level of EU-1 in theproduct. The bulk SiO₂/Al₂O₃ mole ratio and EU-1 content are listed inTable 7 below.

TABLE 7 Example No. 4 5 6 7 8 9 10 11 Percent EU-1 0.25 0.30 2.09 3.133.20 3.22 3.56 6.82 Bulk SiO₂/ 155 88 101 140 130 125 123 118 Al₂O₃ moleratio

The products from Examples 1 and 4-11 were analyzed by XRD and SEM. TheXRD pattern for Example 7 is shown in FIG. 5, and is illustrative of theXRD patterns collected for the remaining Examples 4-11.

The SEM image for Examples 7 and 8 are shown in FIGS. 6 and 7,respectively, and are illustrative of the SEM images for the remainingExamples 4-11. FIGS. 6 and 7 show the SSZ-91 material consists ofpolycrystalline aggregates, each of the aggregates composed ofcrystallites, wherein each crystallite has characteristic average aspectratio of less than 8. In contrast, the ZSM-48 materials of ComparativeExamples 1-3 (FIGS. 2-4) contained long needles and fibrousmorphologies, the presence of which have consistently showed poorcatalytic performance.

Calcination and Ion-Exchange of Molecular Sieves

The as-synthesized products from Comparative Example 1 and Examples 4-11were converted into the sodium form under an atmosphere of dry air at aheating rate of 1° C./min. to 120° C. and held for 120 min followed by asecond ramp of 1° C./min. to 540° C. and held at this temperature for180 min and lastly a third ramp of 1° C./min. to 595° C. and held atthis temperature for 180 min. Finally, the sample was cooled down to120° C. or below. Each of these calcined samples was then exchanged intothe ammonium form as follows. An amount of ammonium nitrate equal to themass of the sample to be exchanged was fully dissolved in an amount ofdeionized water ten times the mass of the sample. The sample was thenadded to the ammonium nitrate solution and the suspension was sealed ina flask and heated in an oven at 95° C. overnight. The flask was removedfrom the oven, and the sample was recovered immediately by filtration.This ammonium exchange procedure was repeated on the recovered sample,washed with copious amount of deionized water to a conductivity of lessthan 50 μS/cm and finally dried in an oven at 95° C. for three hours.

Hydroprocessing Tests

Palladium ion-exchange was carried out on the ammonium-exchanged samplesfrom Examples 1 and 4-11 using tetraamminepalladium(II) nitrate (0.5 wt% Pd). After ion-exchange, the samples were dried at 95° C. and thencalcined in air at 482° C. for 3 hours to convert thetetraamminepalladium(II) nitrate to palladium oxide.

0.5 g of each of the palladium exchanged samples from Example 11 wasloaded in the center of a 23 inch-long by 0.25 inch outside diameterstainless steel reactor tube with alundum loaded upstream of thecatalyst for pre-heating the feed (total pressure of 1200 psig;down-flow hydrogen rate of 160 mL/min (when measured at 1 atmospherepressure and 25° C.); down-flow liquid feed rate of 1 mL/hour. Allmaterials were first reduced in flowing hydrogen at about 315° C. for 1hour. Products were analyzed by on-line capillary gas chromatography(GC) once every thirty minutes. Raw data from the GC was collected by anautomated data collection/processing system and hydrocarbon conversionswere calculated from the raw data.

The catalyst was tested at about 260° C. initially to determine thetemperature range for the next set of measurements. The overalltemperature range will provide a wide range of hexadecane conversionwith the maximum conversion just below and greater than 96%. At leastfive on-line GC injections were collected at each temperature.Conversion was defined as the amount of hexadecane reacted to produceother products (including iso-nC₁₆ isomers). Yields were expressed asweight percent of products other than n-C₁₆ and included iso-C₁₆ as ayield product. The results are included in Table 8.

TABLE 8 Isomerization Percent Selectivity at 96% Temperature C₄-Examples EU-1 (n-C₁₆ Conversion) (° F.) Cracking Example  4 0.25 88% 6061.3% Example  5 0.30 88% 565 1.2% Example  6 2.09 85% 584 1.7% Example 7 3.13 85% 598 1.7% Example  8 3.20 87% 601 1.5% Example  9 3.22 87%597 1.6% Example 10 3.56 86% 600 1.6% Example 11 6.82 82% 593 2.6%

The desirable isomerization selectivity at 96% conversion for thepreferred materials of this invention is at least 85%. A good balancebetween isomerization selectivity and temperature at 96% conversion iscritical for this invention. The desirable temperature at 96% conversionis less than 605° F. The lower the temperature at 96% conversion themore desirable is the catalyst whilst still maintaining isomerizationselectivity of at least 85%. The best catalytic performance is dependenton the synergy between isomerization selectivity and temperature at 96%conversion. A large amount of impurity results in undesirable catalyticcracking with concomitant high gas make reflected in Table 8 byincreased level of C₄ ⁻ cracking. The desirable C₄ ⁻ cracking for thematerials of this invention is below 2.0%. Note the selectivity beginsto decrease at 6.82% EU-1, because increasing concentrations of EU-1promotes catalytic cracking.

Polytype Distribution

Using DIFFaX, simulated XRD patterns for ZSM-48 materials having between70 and 100% polytype 6 were generated and compared to the XRD patterncollected for the molecular sieve product from Examples 8 and 11. Thesimulated and product XRD patterns are presented in FIGS. 8 and 9herein, respectively. A comparison of the product XRD pattern to thesimulated patterns indicates the product synthesized in Examples 8 and11 contained greater than 90% polytype 6.

Using DIFFaX, simulated XRD patterns for ZSM-48 materials having between70 and 100% polytype 6 were generated and compared to the XRD patterncollected for the molecular sieve product from Comparative Example 1.The simulated and product XRD patterns are presented in FIG. 10 herein.A comparison of the product XRD pattern to the simulated patternsindicates the product synthesized in Comparative Example 1 contained 80%polytype 6.

The material synthesized in Comparative Example 1 was subjected to thehexadecane hydroprocessing test as outlined for Examples 4-11 above. Thematerial from Comparative Example 1 exhibited an isomerizationselectivity of 78% at 96% conversion at a temperature of 614° F. Asindicated in Table 9 below, the C₄ ⁻ cracking was 2.8%. Theisomerization selectivity at 96% conversion for the Comparative Example1 material, having a polytype 6 content of only 80%, was inferior tothose described in Examples 4 through 10, as shown in Table 7 above,even though the material of Comparative Example 1 contained animmeasurable (<1%) amount of EU-1. This indicates that although thematerial of Comparative Example 1 and Example 11 exhibited two of thethree characteristics of SSZ-91 (low aspect ratio, low EU-1 content,high polytype 6 content), the lack of the third characteristiccontributed to the material's poor catalytic performance.

TABLE 9 % Isomerization Poly- Selectivity at type % Aspect 96% (n-C₁₆C₄- Examples 6 EU-1 Ratio Conversion) Cracking Comparative  80 <1 7-1278% 2.8% Example  1 Example  8 >90  3.20 1-4 87% 1.5% Example 11 >90 6.82 2-6 82% 2.6%

Example 12-13 Synthesis of SSZ-91 with Alternate Silica Source

The material of Example 12 was prepared by adding NaOH (50%), de-ionizedwater, CAB-O-SIL M-5 silica (Cabot Corporation) and hexamethoniumbromide (HMB) to an autoclave liner. After all the solids had dissolved,anhydrous, Riedel de Haen sodium aluminate was added. Lastly, slurry ofSSZ-91 similar to the slurry from Example 4 was added. The mixture wasstirred until homogeneous. The composition of the aluminosilicate gelproduced possessed the following mole ratios:

TABLE 10 SiO₂/Al₂O₃ 113.6 H₂O/SiO₂ 23.0 OH⁻/SiO₂ 0.17 Na⁺/SiO₂ 0.17HMB/SiO₂ 0.02 Seed 2.92%

The liner was transferred to an autoclave, which was heated to 160° C.over a period of 8 hours, and stirred at a rate of 150 rpm at autogenouspressure. After 48 hours, the product was filtered, washed withde-ionized water and dried. The resulting solids were determined by XRDto be SSZ-91 and contained a 0.30 wt % of EUO. The bulk SiO₂/Al₂O₃ moleratio was found to be about 102.

The material of Example 13 was prepared by adding NaOH (50%), de-ionizedwater, commercially available NALCO 2327 colloidal silica (40.3% SiO₂)and hexamethonium bromide to an autoclave liner. After all the solidshad dissolved, Al₂(SO₄)₃.18H₂O previously dissolved in some of the waterwas added. The mixture was stirred until homogeneous. The composition ofthe aluminosilicate gel produced possessed the following mole ratios:

TABLE 11 SiO₂/Al₂O₃ 177.7 H₂O/SiO₂ 20.0 OH⁻/SiO₂ 0.13 Na⁺/SiO₂ 0.17HMB/SiO₂ 0.05

The liner was transferred to an autoclave, which was heated to 160° C.over a period of 8 hours, and stirred at a rate of 150 rpm at autogenouspressure. After 35 hours, the product was filtered, washed withde-ionized water and dried. The resulting solids were determined by XRDto be SSZ-91 and contained a 3.16 wt % of EU-1. The bulk SiO₂/Al₂O₃ moleratio was found to be about 155. The material of Example 13 was analyzedby scanning electron microscopy, and an SEM image from that analysis isshown in FIG. 11.

Hydroprocessing Tests

For the SSZ-91 materials synthesized in Examples 12 and 13, palladiumloading and catalytic tests were carried out as described with respectto the Examples above. The results of the catalytic tests are shownbelow in Table 12. These two examples prepared by varying the rawmaterials used show the versatility of SSZ-91 preparations. Example 12showed another good example of desirable isomerization selectivity, 88%at significantly lower temperature at 96%. Example 13, although phasepure, but showed inferior catalytic performance, a result of the crystalhabit with poor aspect ratio of the crystals.

TABLE 12 % Isomerization Poly- Selectivity Temper- C₄- Percent Aspecttype at 96% (n-C₁₆ ature minus Example EUO Ratio 6 Conversion) (° F. )Cracking Example 12 0.30 1-3 >90 88% 559 1.3% Example 13 3.16 >10 >9078% 587 2.2%

Using DIFFaX, simulated XRD patterns for ZSM-48 materials having between70 and 100% polytype 6 were generated and compared to the XRD patterncollected for the molecular sieve product from Example 13. The simulatedand product XRD patterns are presented in FIG. 12 herein. An SEM imagefrom that analysis is shown in FIG. 11A comparison of the product XRDpattern to the simulated patterns indicates the product synthesized inComparative Example 1 contains greater than 90% polytype 6. Thisindicates that although the material of Example 13 had the requisite lowEU-1 content and desired polytype distribution, the high aspect ratiocontributed to the material's poor catalytic performance. Example 13again demonstrates that the lack of any one of the three characteristicsof SSZ-91 (low aspect ratio, low EU-1 content, high polytype 6 content)contributes to the material's poor catalytic performance.

What is claimed is:
 1. A hydroprocessing catalyst comprising a molecularsieve belonging to the ZSM-48 family of zeolites, wherein the molecularsieve comprises: at least 70% polytype 6 of the total ZSM-48-typematerial present in the product, and an additional EUO-type molecularsieve phase in an amount of between 0 and 3.5 percent by weight of thetotal product; and wherein the molecular sieve has a morphologycharacterized as polycrystalline aggregates comprising crystallitescollectively having an average aspect ratio of between 1 and 8, andwherein the catalyst further comprises one or more Groups 8 to 10 metalsof the Periodic Table.
 2. The catalyst of claim 1, wherein the molecularsieve has, in its as-synthesized form, an X-ray diffraction patternsubstantially as shown in the following Table: 2-Theta d-spacing (nm)Relative Intensity^((b))  7.55 ± 0.20 1.170 W  8.71 ± 0.20 1.015 W 12.49± 0.20 0.708 W 15.12 ± 0.20 0.586 W 21.18 ± 0.20 0.419 VS 22.82 ± 0.200.390 VS 24.62 ± 0.20 0.361 W ^((b))W = weak (>0 to ≤20); M = medium(>20 to ≤40); S = strong (>40 to ≤60); VS = very strong (>60 to ≤100).


3. The catalyst of claim 1, wherein the molecular sieve has a siliconoxide to aluminum oxide mole ratio of 40 to
 220. 4. The catalyst ofclaim 1, wherein the molecular sieve has a silicon oxide to aluminumoxide mole ratio of 70 to
 160. 5. The catalyst of claim 1, wherein themolecular sieve comprises at least 80% polytype 6 of the totalZSM-48-type material present in the product.
 6. The catalyst of claim 1,wherein the molecular sieve comprises between 0.1 and 2 wt. % EU-1. 7.The catalyst of claim 1, wherein the crystallites collectively have anaverage aspect ratio of between 1 and
 5. 8. The catalyst of claim 1,wherein the molecular sieve comprises at least 90% polytype 6 of thetotal ZSM-48-type material present in the product.
 9. The catalyst ofclaim 1, wherein the crystallites collectively have an average aspectratio of between 1 and
 3. 10. The catalyst of claim 1, wherein the metalcomprises nickel, platinum, palladium, or a combination thereof.
 11. Amethod of preparing a catalyst comprising the molecular sieve of claim1, the method comprising loading the molecular sieve with one or moreGroups 8 to 10 metals by impregnation or ion-exchange.
 12. The method ofclaim 11, wherein the molecular sieve is prepared from a reactionmixture comprising at least one source of silicon, at least one sourceof aluminum, at least one source of an element selected from Groups 1and 2 of the Periodic Table, hydroxide ions, hexamethonium cations, andwater; and the reaction mixture is subjected to crystallizationconditions sufficient to form crystals of the molecular sieve.
 13. Themethod of claim 12, wherein the molecular sieve is prepared from areaction mixture comprising, in terms of mole ratios, the following:SiO₂/Al₂O₃  50-220 M/SiO₂ 0.05-1.0  Q/SiO₂ 0.01-0.2  OH/SiO₂ 0.05-0.4 H₂O/SiO₂  3-100

wherein M is selected from the group consisting of elements from Groups1 and 2 of the Periodic Table; and Q is a hexamethonium cation.
 14. Themethod of claim 12, wherein the molecular sieve is prepared from areaction mixture comprising, in terms of mole ratios, the following:SiO₂/Al₂O₃  85-180 M/SiO₂ 0.1-0.8 Q/SiO₂ 0.02-0.1  OH/SiO₂ 0.10-0.3 H₂O/SiO₂ 10-50

wherein M is selected from the group consisting of elements from Groups1 and 2 of the Periodic Table; and Q is a hexamethonium cation.
 15. Themethod of claim 11, wherein the molecular sieve is combined with amatrix material prior to loading with one or more Groups 8 to 10 metals.16. A process for converting hydrocarbons, comprising contacting thecatalyst of claim 1 with a hydrocarbonaceous feed under hydrocarbonconverting conditions.